The present invention relates to a connecting rod for use in a steering portion, stabilizer portion and the like of a vehicle, and more particularly to a connecting rod having a pair of ball joints on both ends of a rod main body and in which shanks swingably provided on the ball joints are disposed such that axes thereof intersect each other at 90xc2x0.
Conventionally, this kind of the connecting rod has been disclosed in Japanese Patent Application Laid-Open No. 10-59206. This connecting rod is so constructed by connecting two ball joints 110, 111 in which a holder is connected to a shank in a different way as shown in FIG. 5. That is, in the ball joint 110, the holder 112 is connected to the ball-shank 113 in a substantially L-shape and in the other ball joint 111, the holder 114 is connected to the ball-shank 115 in a substantially I-shape. By connecting the holder 112 of the ball joint 110 to the ball-shank 115 of the ball joint 111, a substantially L-shaped connecting rod in which a pair of the ball-shanks are disposed such that their axes intersect each other at 90xc2x0 is formed.
However, upon manufacturing the substantially L-shaped connecting rod by connecting the two ball joints, a distance between the center of swings of the ball joints or a distance between the centers has to be adjusted at the time of connecting the ball joints, so that the connecting work becomes complicated. Further, two kinds of the ball joints have to be manufactured because the connecting styles of the holder and ball-shank are different. As a result, numbers of necessary parts and manufacturing steps increase thereby leading to an increase of production cost.
On the other hand, Japanese Patent Application Laid-Open No. 63-28710 has disclosed a connecting rod in which a pair of ball joints are formed integrally by aluminum die casting. This connecting rod, as shown in FIG. 6, comprises a rod main body 105 having a pair of ball-shanks 102 in which a ball portion 101 is formed at a front end of a shank portion 100 and a pair of socket portion 104, 104 provided at both ends of a shaft portion 103 for accommodating a ball portion 101 of each of the ball-shank 102. Socket portions 104 of the rod main body and shaft portion 103 are formed integrally by aluminum die casting. The ball portion 101 of each ball-shank 104 is accommodated in the socket portion 104 of the rod main body 105 together with bearing 106 made of synthetic resin. As a result, the shank portions 102 of the ball-shank 102 are swingable with respect to each of the aforementioned socket portions 104, so that the ball joints are formed on both ends of the rod main body 105.
However, if it is intended to produce a connecting rod in which a rod main body thereof is made of aluminum diecast and a pair of ball joints are connected in a substantially L shape, of a pair of the socket portions 104, 104 provided on the rod main body 105, one socket portion 104 has to be open in an axial direction of the rod main body 105, so that strength of the ball joint to be assembled by the socket portion 104 is short. That is, in a ball joint which is connected to the rod main body 105 in line, the ball portion 101 has to be encased in the socket portion 104 against an axial force applied to the ball-shank 102 and an axial force applied to the rod main body 105. However, because the socket portion 104 is open in the axial direction of the rod main body 105, if an excessive force is applied thereto, the ball portion 101 may escape from the socket portion 104 together with the bearing 106. Therefore, upon manufacturing a connecting rod in which a pair of the ball joints are connected in a substantially L shape, it is difficult to construct the ball joint by forming a pair of the socket portions in the rod main body as disclosed in Japanese Patent Application Laid-Open No. 63-28710.
Accordingly, the present invention has been accomplished in views of these problems and therefore, it is an object of the invention to provide a connecting rod in which a pair of ball-shanks are connected to a rod main body such that they are axially perpendicular to each other, having a sufficient strength and which can be manufactured easily and at a low cost, and a manufacturing method of the same.
To achieve the above object, the present invention provides a connecting rod comprising first and second ball-shanks in which a ball portion is formed at a shank portion each of thereof; a rod main body having first and second ball receiving portions for holding the ball portions of the first and second ball-shanks, having a joint portion which has the ball receiving portions at both ends thereof, and connected the first or second ball-shanks freely swingably and rotatably; and wherein said first ball-shank is connected to said rod main body such that the shank portion thereof is perpendicular to the joint portion, while said second ball-shank is connected to said rod main body such that the shank portion thereof is parallel to the joint portion, and said rod main body is die-cast with the ball portion of the ball-shank being inserted as core, so that said first ball receiving portion, second ball receiving portion and joint portion are integral.
In the connecting rod of the present invention having such a structure, a rod main body for connecting a pair of the ball-shank is formed by die-casting with the ball portion of each ball-shank being inserted as a core. Thus, the ball portion is encased by the ball receiving portion of the rod main body, so that the ball-shank is firmly connected to the rod main body. Because the rod main body is cast such that the ball portion of the ball-shank is encased therein, a procedure for connecting the ball portion of the ball-shank to the rod main body such that they are freely swingable is eliminated, thereby making it possible to manufacture the connecting rod easily at low cost.
On the other hand, as for a manufacturing method of the connecting rod of the present invention having such a structure, if the aforementioned first and second ball-shanks are connected to the rod main body such that they intersect the joint portion of the rod main body, the rod main body in which the ball is encased by the ball receiving portion can be produced using the manufacturing method described in Japanese Patent Application Publication No. 5-7786. That is, according to this disclosed manufacturing method, upon casting a holder with a ball inserted into a cast die as a core, the ball is sandwiched by a pair of the supporting portions projecting from the die so that it is not moved in the die. When the ball joint is completed, the shank portion of the ball-shank projects from the opening portion formed in the holder by this supporting portion. Therefore, if a pair of the ball-shanks are parallel to each other in a connecting rod of the present invention, the opening portions of the pair of the opening portions formed in the rod main body have only to be open in the same direction, so that upon casting of the rod main body, the ball can be fixed in the die easily.
However, in a connecting rod of the present invention, as described above, the first ball-shank intersects the joint portion of the rod main body and the second ball-shank is parallel to the joint portion of the rod main body. That is, the first ball-shank and second ball-shank are axially perpendicular to each other. Therefore, the opening portions to be provided in the rod main body for the ball-shanks need to be open in directions perpendicular to each other and a pair of the balls inserted into the casting die must be sandwiched from opposite directions. Thus, upon manufacturing of the connecting rod of the present invention, the manufacturing method described in Japanese Patent Application Publication No. HEI5-7786 cannot be just applied and a new manufacturing method needs to be invented by improving the aforementioned manufacturing method in order to die-cast the rod main body with a pair of the balls fixed securely in the casting die.
That is, the present invention provides a manufacturing method of a connecting rod for connecting first and second ball-shanks swingably and rotatably on both ends of a rod main body such that shanks thereof are perpendicular to each other, the manufacturing method comprising: first step for closing first and second die half bodies, inserting a first ball into a cavity formed in the die half bodies and fixing a first ball in the cavity with a first supporting portion projecting from the die half bodies; second step for closing a third die half body with respect to the closed first and second die half bodies in a direction perpendicular to the closing direction of the first and second die half bodies, inserting a second ball into a cavity formed by the three die half bodies, and fixing the second ball in the cavity with the second supporting portion projecting from the first and second die half bodies and third supporting portion projecting from the third die half body; third step for casting the rod main body holding the first and second balls and in which opening portions communicating with each of the balls are formed corresponding to the first-third supporting portions by pouring molten metal into cavities in casting dies formed by closing the respective die half bodies; fourth step for forming the first and second ball-shanks by joining the shank to each of the balls in the rod main body via an opening portion formed in the rod main body by the first-third supporting portions; and fifth step for forming a gap between each ball and rod main body by providing the rod main body and each ball-shank with an external force.
According to this manufacturing method, the die for casting the rod main body is divided to the first-third die half bodies and, of a pair of the balls to be inserted into cavities of the die half bodies, the first ball is sandwiched by the first supporting portion projecting from the first and second die half bodies, and the second ball is sandwiched by the second supporting portion projecting from the first and second die half bodie and the third supporting portion projecting from the third die half body. Therefore, the ball never shakes when molten metal is poured into the cavity and the rod main body can be cast in such a condition that these balls are held securely at each predetermined position in the cavity. As a result, a gap between the ball and ball receiving portion formed in the rod main body is eliminated, so that smooth rotation and swing of the ball-shank with respect to the rod main body are ensured.